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Attic sealing with existing loose fill insulation – practical advice

sippycup | Posted in Energy Efficiency and Durability on

Hey all, I previously posted about my new old 1943 house in East TN (1200 sqft original with a 350 sqft vaulted addition, crawl space, in Climate Zone 4). I recently closed on the house and am assessing how I’m going to address the “invisible” issues – this week I’m obsessing about the attic (vented and unfinished). I have very little contruction experience but am learning as I go, and my thermo knowledge is pretty strong.  

The house has a vented attic (ridge vent, soffit vents, and gable vents) and has some combination of faced cellulose batts and loose fill as well as faced fiberglass batts in the attic. Appears to be a collection of legacy (batts) and new (loose fill) efforts. Combined insulation highest point is maybe 2′, but average height is closer to 1′. Miscellaneous decking for storage/walking has been installed around the attic entrance with batts underneath. HVAC is a 10-year old Trane unit (no natural gas heating, will upgrade to gas pack when it bites the dust) and a wood stove backfitted into the original masonry fireplace.

I understand that air sealing is very important from reading several GBA articles, especially at the ceiling/attic interface. The extent of air sealing (e.g. around the masonry fireplace, top plates of walls, electrical holes in top plates) is unknown, but I’m assuming the worst. I haven’t dug past the insulation yet to verify but I will. Let’s just say the ceiling attic door is totally without weatherstripping or insulation so it’s rather unlikely that the homeowner or any contractor performed methodical air sealing at the ceiling/attic interface.

So when I dig past the batts and see that nothing has been sealed, I plan on doing it myself. My eventual game plan after sealing would be to attain a high R value with additional or new loose fill cellulose (don’t plan on attic storage).  I have a few practical questions I was curious if anyone could help me with:

1. A few Youtubers have opted to remove ALL existing loose fill from their attic using vacuum rigs, e.g. and . Another option I can think of working on one zone at a time after moving the loose fill (say with a snow shovel and/or rake into trash bags) and batts in that zone aside, then replacing the insulation after finishing sealing each zone. I’m sort of worried that I might be overly optimistic on my zone approach and was curious what other folks might think?

I guess I could give it a shot first. The loose fill vacuum removal approach would cost more and require additional logistics (outdoor “insulation catch” for instance) but if it’s best for some reason I’m not considering now then I could be persueded to go that route. For instance, I know that fiberglass loose fill compacts over time, so some people might just want to ditch it entirely, but it seems more reasonable to just blow in additional cellulose fill on top.

2. I’m having a tough time finding well-reasoned recommendations for caulk and/or expanding foam products for attic applications. Does anyone have any experience here?

3. It’s pretty warm  right now but will begin getting into sub-freezing weather soon. I’m curious if the foam/caulk I use will run into curing issues as a result of the temperature – any comments here? Obviously I would also check the spec sheets of the products I choose.

4. Any other considerations to think about? I plan on wearing a P100 respirator, putting down OSB/plywood sheets across the ceiling joists to stand/sit on, etc.

Thank you very much!

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  1. joshdurston | | #1

    I'm curious too, I have the same mix of faced fiberglass and loose fill cellulose. I'm considering ditching the faced batts, since they are tougher to reinstall effectively in the ceiling joists space. Then after sealing things up, topping off with with more cellulose.

  2. seabornman | | #2

    I've done this by moving insulation aside, doing air sealing, then pushing insulation back. Typically, you're just trying to find the top plate of walls below and ceiling j-boxes, which is not a large percentage of attic space. Be careful at fireplace and any flues coming up through attic. There are rules about combustible products and their proximity depending on type of penetration. The biggest pain is sealing at the bearing plate for trusses/rafters. You can take care of properly installing baffles, etc. while you are lying face down in the insulation getting poked by roofing nails. Have fun!

  3. michiganman18 | | #3

    I can really only help with the caulk/sealant recommendation.

    For drywall/electric boxes near the interior(below the insulation, near drywall, etc) I used titebond sound and smoke. It was around 5.00 per 28oz tube. It stays flexable to move with temp changes/and stops air/sound as much as a product like this can. It is not tacky once cured. I have not used the more expensive trusted products often mentioned here. This product is close to 0SI SC175, but cheaper, and low VOC.

    For the exterior, or futher from condition space I used OSI quad caulk. Stays flexible, very strong, good for moisture, and any other applications. I didnt need much it as was mostly protected environment. I tape and caulk for electrical boxes. the Quad, is able to be applied below freezing and is freeze thaw stable. The titebond is able to be applied at 40F, and freeze thaw stable in a few hours.

    As long as the temp is in the zone, and you check the spec sheet you will be fine. Not a place to overthink this.

    Also, please make sure that due to the age of your house, you dont have vermiculite insulation like many older homes do. It most likely contains asbestos, and requires additional precautions for yourself, family, and those around. Make sure you have a good fit on the respirator or its practically useless. Also, I would shut off, or turn down your HVAC while you are doing this, and if its above freezing, install a fan in a window, effectively making a blower door to have positive pressure within the house so dust exits the house.

    Hope this helps with the sealant situation.

  4. walta100 | | #4

    This house is likely to be very leaky if you are going to seal it up. You need a way to find and see the leaks. Blindly calking will be difficult and unsatisfying work as cannot see any immediate improvement.

    I like to depressurize the house with a fan and use smoke from incense sticks.

    This link may be helpful.


  5. GBA Editor
    Martin Holladay | | #5

    Sippy Cup,
    I advise you to read this article: "Air Sealing an Attic."

  6. Yupster | | #6

    I recently performed this work on my own house with the same situation. I opted to rake the cellulose aside wherever there was a top plate and move the batts out of the attic. Raking or shoveling the cellulose causes it to fluff up a LOT and even though I only had a couple inches existing, I barely had enough room in a reasonably sized attic to move it all aside ahead of time. I used a froth-pak of CCSPF to seal every top plate or penetration. You can' t stop spraying for more than a few seconds, so everything has to be exposed ahead of time. It took me days to do it by myself. Getting down to the eaves to construct an airtight baffle was too difficult/painful, so I decided to do that when I replace the soffit. Laying down a sheet of foam cut to size over any interior soffits exposed to the attic and foaming the edges was easy enough. I don't think removing it all and then re-installing it would have been any less work, but it might have meant less time in the sweltering attic moving insulation back and forth!

  7. Jon_R | | #7

    +1 on directed air sealing vs just guessing.

  8. sippycup | | #8

    Hey guys, I really appreciate the advice!

  9. Andrew_C | | #9

    Wrt air sealing with foam in attic - you may want to read up on using a water mister to get the most out of your foam. [Jan 21, 2014, Martin Holladay article testing Justin Fink's foam advice.] The visuals in that article tell a story. And as pointed out in the comments, cold air is dry air, so misting with water may be even more important if you're working with moisture-cured foam in cold weather.

    1. sippycup | | #10

      Ah, very timely advice, thank you!

      One additional question comes to mind - would you guys recommend waiting for the nominal cure time prior to placing attic insulation back on top of caulk or foam? Or just wait until no longer "tacky?"

  10. michiganman18 | | #11

    Depending on the caulk it may stay tacky. Depending on the product it may not cure without some air.

    That said. It would probably be fine. But why cut your legs out from underneath you when you could just wait a little longer. If its colder it will most likely take longer.

  11. Expert Member
    BILL WICHERS | | #12

    Ah, you are about to begin your attic adventure. Attic work is a huge pain, so make sure you prepare so you can do as much as possible in as few trips as possible.

    Your respirator is a good idea. You will also want a few tyvek suits and some duct tape. Get the full suits with hoods and footies. You want several suits because they’ll tear while you work, so you’ll get a day out of a suit at best and you probably have several days of work to do. Use the duct tape to seal the footies. You don’t want any blown insulation getting to your skin because you’ll itch like crazy. Safety goggles, not glasses, are good too but they fog easily so bring a paper towel or rag with you where you can reach it from outside the suit to wipe the goggles off. They fog inside too, so be ready for that.

    Wear some comfy leather work gloves. Leather gloves are best, anything knit will get itchy and full of insulation bits and you’ll end up throwing it in the trash.

    Have several good work lights with cords (NOT cordless), and hang them to light as much as you can before you start work with the cords out of the way. Have one really good cordless light with you as you crawl around that you can use to point at things. I really like the big LED floodlight that ryobi makes, and it’s pretty cheap. A big flashlight works too. The main thing is you want a powerful cordless light with a long battery life.

    Have any tools you need handy and nearby. Backing up while crawling around is a big pain, try to work in one direction as much as possible with the least amount of turning around and doubling back. Have more of whatever consumables you need than you think you’ll use, running out of any caulk/greatstuff/etc Means another trip to the attic after you get more. You will soon come to loathe trips to the attic.

    Be very careful moving around in the attic. Rafters And chords of trusses will hold you up. A slip of the boot and a foot through the drywall ceiling and you’ll have some patching to do AND a big mess to clean up. You’ll be tired after the attic work and won’t be wanting to clean up a mess of drywall and insulation. A piece of 3/4” plywood big enough to span about 1.5x the distance between supports and maybe 16-18” wide makes a handy mobile work platform. You can use a piece of 2x10 or 2x12 too, but the plywood is a lot lighter. Two pieces of plywood let’s you leapfrog around.

    On the plus side, the work itself is not complicated, it’s just tedious. You can do a good job yourself. Just be careful, be prepared, and WEAR THE TYVEK SUIT. Trust me on this, laying in blown in fiberglass will make you itch for days without the suit. I’ve been there, don’t be like me :)

    When you’re all done, take a cold shower, then a hot shower, and maybe a cold shower again. The cold/hot cycle helps to open and close the pores of your skin to get any fibers out. Wash your work clothes seperate from your other laundry and throw the Tyvek suit in the trash. Attic work is not fun, but you can accomplish a lot with minimal special tools or skills so it’s a great DIY project.


    1. sippycup | | #13

      Bill, thank you very much, excellent and voluminous advice. I was just planning on doing the job in my polyester coveralls, but the Tyvek suits with head/neck protection will be much better and look pretty economical... definitely will grab a few of these!

      I'm planning on using Sachco Big Stretch for 1/4" and less cracks, and something like Great Stuff foam for larger gaps. Do you guys think I can reuse these products in my crawlspace for mud sill/joist sealing, foundation CMU block sealing, etc.? Planning on sealing down there plus a vapor barrier on the dirt and up the foundation wall, foundation wall interior side insulation, etc.

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